5B42 Isolated, Process Current Input
Functional Description
The 5B42 is a single-channel signal conditioning module that interfaces with two-wire
transmitters, providing an isolated, regulated 20 V supply voltage. The module filters and
amplifies the 4-to-20 mA process-current input to produce an accurately scaled, low-noise
low-impedance output of +1 to +5 V or +2 to +10 V.
True Three-Port Isolation
The floating, differential input circuit on the field side eliminates the need for any input
grounding. Signal and power isolation by transformer coupling uses a proprietary
modulation technique for linear, stable and reliable performance. A demodulator on the
computer side of the signal transformer recovers the original signal, which is then filtered
and buffered to provide a low-noise, low-impedance output signal. True three-port
isolation (Input-Output-Power) includes common-mode ratings of: 1500 V rms between
input and output and input and power; 250 V rms between power and output - no return
path is required between the power and signal output commons.
Accurate and Stable Performance
The 5B42 maintains accuracy over the wide operating temperature range of -40°C to +85°C through design for low parameter drift. This
enables the module to provide output offset drift of only ±5 µV/°C and gain drift of just ±25 ppm/°C.
Why an Internal Current Sense Resistor
The 5B42 offers significant advantages over signal conditioners that require an external current sense resistor. First, an external resistor
is not protected from accidental connection to a 240 V rms power line. Next, the external resistor tolerance must be added to the
conditioners specified errors. In contrast, the 5B42 is calibrated and specified with its internal 25
sense resistor. Further, the 5B42
signal input, loop supply and the sense resistor are all protected against accidental application of excess voltages up to 240 V rms.
Finally, there is no need to install an external sense resistor on the backplane, but if one is installed it will not affect 5B42 performance.
Filtering and Protection
The 5B42 contains an optimized five-pole low-pass filter with a -3 dB bandwidth at 100-Hz that provides a low-overshoot step response
and exceptionally low noise of 200 µV pk-pk in a 100 kHz bandwidth. Attenuation (normal mode rejection) increases at a 90 dB/decade
rate beyond 100 Hz.
The module protects the computer side from damage due to field-side overvoltage faults. The module withstands 240 V rms at the input
terminals without damage, thereby shielding the internal computer-side circuitry from field-side overvoltage conditions. In addition, the
5B42 is mix-and-match and hot-swappable with all other 5B Series modules, so can be inserted or removed from any socket in the same
backplane without disrupting system power.
Convenience Features
A series output switch eliminates the need for external multiplexing in many applications. The switch is turned on by an active-low enable
input. If the switch is to be on at all times, the enable-input should be grounded to output common as it is on the 5B01 and 5B08
backplanes.
Figure 1. 5B42 Functional Block Diagram
Input Ranges
Two-Wire Transmitters 4 to 20 mA
(0 to 20 mA - custom)
Output Range
+1 to +5 V or +2 to +10 V
(0 to +10 V - custom)
5B42 Models Available
Model
Input Range Output Range
5B42-01
4 mA to 20 mA
+1 V to +5 V
5B42-02
4 mA to 20 mA
+2 V to +10 V
5B42-Custom
*
*
* Custom Input/Output ranges are available.
Refer to ordering guide.
Figure 2. 5B42 Input Field Connections
5B42 Specifications
(typical @ +25°C and Vs = +5 V dc)
Description
Model 5B42
Input Ranges
Standard Ranges
4 mA to 20 mA (Refer to Model Table)
Custom Ranges
0 mA to 20 mA (Refer to Ordering Section)
Isolated Loop Supply Voltage
20 V @ 4 mA to 20 mA Input
Output Ranges (RL > 50 k
)
+1 V to +5 V; +2 V to +10 V
Accuracy1
Initial @ +25°C
±0.05% Span ±4 µA RTI
Nonlinearity
±0.01% Span
Input Offset vs. Temperature
±0.5 µV/°C
Output Offset vs. Temperature
±5 µV/°C
Gain vs. Temperature
±0.0025% of Reading/°C
Input Sense Resistor
2
25
Noise
Input, 0.1 Hz to 10 Hz Bandwidth
10 nA rms
Output, 100 kHz Bandwidth
200 µV peak-peak
Bandwidth, -3 dB
100 Hz
Output Step Rise Time, 10% to 90% Span
4 ms
Common-Mode Voltage (CMV)
Output-to-Input, Continuous
1500 V rms, maximum
Input-to-Power, Continuous
1500 V rms, maximum
Output-to-Power, Continuous3
250 V rms, maximum
Transient
ANSI/IEEE C37.90.1-1989
Common Mode Rejection (CMR)
1k
Source Imbalance, 50/60 Hz
Normal Mode Rejection (NMR)
140 dB
-3 dB @ 100 Hz (90 dB per decade > 100 Hz)
Input, Excitation, and Sense Resistor Protection
Continuous
240 V rms, maximum
Transient
ANSI/IEEE C37.90.1-1989
Output Resistance
25
Voltage Output Protection
Continuous Short to Ground
Output Current Limit
±20 mA
Output Selection Time
6 µs to ±1 mV of Vout @ Cload = 0 to 2,000 pF
Output Enable Control3
Max Logic "0"
+0.8 V
Min Logic "1"
+2.4 V
Max Logic "1"
+36 V
Input Current "0", "1"
0.5 µA
Power Supply Voltage
+5 V dc ±5%
Power Supply Current
@ Transmitter Load of 20 mA
200 mA
@ Transmitter Load of 4 mA
100 mA
Power Supply Sensitivity, RTI
±1 µV/% of Vs
Mechanical Dimensions
2.275" x 2.375" x 0.595"
(57.8 mm x 59.1 mm x 15.1 mm)
Environmental
Temperature Range
Rated Performance
-40°C to +85°C
Operating
-40°C to +85°C
Storage
-40°C to +85°C
Relative Humidity
0 to 95% @ +60°C, noncondensing
RFI Susceptibility
±0.5% Span error @ 400 MHz, 5 Watt, 3 ft